Conventional liquid crystal display devices include the TN (Twisted Nematic) type and the STN (Super Twisted Nematic) type, both using nematic liquid crystal. These types require polarizers, which causes a problem in that the brightness of the display becomes less. Furthermore, since the thickness of the cell must be accurately controlled, it is difficult to enlarge the screen, and the view angle is narrow.
To solve these problems and provide a low-cost liquid crystal display device with a large, bright screen having a high contrast ratio, research has been conducted on the application of polymer dispersed types or polymer+liquid crystal composite systems to liquid crystal devices. Most of the display devices developed to date that use polymer dispersed types or polymer+liquid crystal composite systems employ nematic liquid crystal as the liquid crystal component. The response speeds of these display devices are considerably low compared to other liquid crystal display devices, while a voltage for driving them is relatively higher.
Regarding another matter, research has also been conducted on polymer+liquid crystal composite systems using cholesteric liquid crystal as the liquid crystal component. Above all others, the PCW (Polymer Cell Wall) type liquid crystal optical shutter, which is disclosed in the Japanese Patent No. 3030973 (Tadahiro Asada), has exhibited considerable improvement in respect to the contrast ratio and the response speed. This type is now at the level of practical application.
In scattering types, however, it is necessary to use subtractive color mixing to display colors. This means that a laminated cell structure or similar structure is required. Also, while the display becomes brighter, there is a problem in that its producing consumes time and labor.
The present invention provides improvements in the aforementioned aspects, and its objective is to provide a liquid crystal display device for displaying colors by transmission and reflection modes and a method for producing such devices, whereby the additive color mixing can be used, the structure is simplified, the driving-voltage is lower, the contrast is higher, the response speed is higher, and the screen can be larger.
In general, devices currently called “reflection type” are constructed so that a reflector is located at the back of the device to reflect light, the reflected light is guided to pass through color filters corresponding to three primary colors, and the three primary colors are blended to display colors. The principle used in this type is the same as that used in the transmission type; the only difference is that one type uses direct light from the light source whereas the other type uses reflected light. Accordingly, in this specification, it is assumed that the term “transmission type” includes the reflection type.